Complete with BE (in the past) + V-
ing.
1. 
  Romeo 
 (dance) with Rosaline when he saw Juliet.
2. 
Describe a past activity
 Use BE in the past + V-
ing to describe an action
 that was in progress (not finished) at a specific time in the past. 
3. 
  Tybalt and Mercutio (fight) 
 when Romeo came to stop them.
  
4. 
   (Juliet sleep) when Romeo arrived with the poison?
 
  
Use BE in the past + V-ing to describe an action that was in progress (not finished) at a specific time in the past.